This invention relates to the copolymerization of dicyclopentadiene with norbornene derivatives and to copolymers obtainable thereby. In one aspect, the invention relates to the copolymerization of dicyclopentadiene with bulky norbornene monomers to provide copolymers showing tailored product properties such as increased glass-transition temperatures.
Processes for copolymerization of dicyclopentadiene with relatively bulky norbornene monomers by ring-opening polymerization are known from, e.g., Japanese patent application No. 61293208, U.S. Pat. No. 4,568,660, U.S. Pat. No. 3,718,474 and European patent No. 142,861.
Japanese patent application No. 61293208 discloses production of a copolymer by ring opening and copolymerization by a reaction injection moulding (RIM) process of at least two norbornene type monomers in the presence of a catalyst containing an inorganic tungsten compound and an activator to form a molded copolymer showing acceptable thermal resistance. Particularly disclosed comonomers are, e.g., tetracyclododecene, methyltetracyclododecene, dimethyltetracyclododecene, ethyltetracyclododecene and propyltetracyclododecene, and preferably at least one of 2-norbornenes and dicyclopentadiene and at least one tetracyclododecene are used in a ratio of 5-8% by weight and 20-95% by weight, respectively, for a copolymerization using a tungsten compound such as WCl.sub.6 or WOCl.sub.4 and an activator such as a dialkylaluminium monohalide, an aluminium sesquihalide, a trialkylaluminium and/or an aluminum trihalide as metathesis catalyst system.
U.S. Pat. No. 4,568,660 discloses, in column 32, lines 58-68 and in column 33, lines 1-32, respectively, the addition of a comonomer that will either have two or more strained, reactive double bonds that will open during the polymerization, in order to increase the number of crosslinks, or a comonomer which contains four or more rings so that rotation or movement of the resulting backbone will be more constrained, in order to reach a raised Tg of the polymer. As examples of useful norbornene type monomers are mentioned 1:1 Diels-Alder adducts of cyclopentadiene with norbornene, norbornadiene and 1,5-cyclooctadiene, the adducts of cyclopentadiene with polyfunctional acrylates such as trimethylolpropane triacrylate and the like, and the 2:1 adduct of cyclopentadiene with diallyl adipate. Substantial increases in the crosslink density (as measured by the degree of swelling of the copolymers) are reported with copolymers made from dicyclopentadiene (DCPD) and the cyclopentadiene adducts with norbornadiene, trimethylpropane triacrylate, ethylene glycol diacrylate and ethylene glycol dimethacrylate.
U.S. Pat. No. 3,718,474 at column 4, lines 52-58discloses the preparation of a copolymer of DCPD and acenaphthylene to be used in an exposure assembly for imagewise exposing of a layer of a solid soluble polymer that becomes crosslinked to an insoluble condition at sites of exposure to light.
European patent No. 142,861 discloses a RIM method for making a crosslinked thermoset polymer containing units derived from DCPD, catalyzed by a metathesis catalyst system which includes an organoaluminium or alkylaluminium halide activator. In this method, not more than 20% of the DCPD units are replaced by other polymerizable units and the catalyst is a pentavalent tantalum catalyst represented by the formula Ta--Y.sub.5, wherein --Y is a) a halide, b) an alkoxy having the formula --O--R in which the organic radical R is a hydrocarbyl containing from 1 to 10 carbon atoms, c) an aryloxy having the formula --O--Ar, wherein the radical Ar is an aromatic radical containing from 1 to 3 aromatic rings, or d) an acyloxy having the formula OOCR.sup.1, in which the organic radical R.sup.1 is a hydrocarbyl containing from 1 to 10 carbon atoms. The other cycloolefin monomers are selected from norbornene, norbornadiene, cyclopentene, dimethanehexahydronaphthalene and dimethaneoctahydronaphthalene.
There remains a need for an economical process for the manufacture of crosslinked thermoset polymers based on DCPD having tailored product properties, such as higher glass transition temperatures.
It is therefore an object of the invention to provide an improved process for preparing DCPD-based polymers.